SHIFT WORK DISORDER - myCME.com

Circadian Adjustment and Permanent Night WorkA Compromise Circadian Phase Position for Permanent Night Work ImprovesMood, Fatigue, and PerformanceMark R. Smith, PhD, RPSGT; Louis F. Fogg, PhD; Charmane I. Eastman, PhDBiological Rhythms Research Laboratory, Department of Behavioral Science, Rush University Medical Center, Chicago, ILStudy Objective: To assess night shift improvements in mood, fatigue, and performance when the misalignment between circadian rhythms anda night shift, day sleep schedule is reduced.Design: Blocks of simulated night shifts alternated with days off. Experimental subjects had interventions to delay their circadian clocks to partiallyalign with a night shift schedule. Control subjects had no interventions. Subjects were categorized according to the degree of circadian realignmentindependent of whether they were in the experimental or control groups. Twelve subjects were categorized as not re-entrained, 21 as partially reentrained,and 6 as completely re-entrained.Setting: Home sleep and laboratory night shifts.Participants: Young healthy adults.Interventions: Experimental subjects had intermittent bright light pulses during night shifts, wore dark sunglasses outside, and had scheduledsleep episodes in darkness.Measurements and Results: A computerized test battery was administered every 2 hours during day and night shifts. After about one week onthe night shift schedule, which included a weekend off, the partially and completely re-entrained groups had markedly improved mood, fatigue, andperformance compared to the group that was not re-entrained. The completely and partially re-entrained groups were similar to each other and hadlevels of mood, fatigue, and performance that were close to daytime levels.Conclusions: Partial re-entrainment to a permanent night shift schedule, which can be produced by feasible, inexpensive interventions, is associatedwith greatly reduced impairments during night shifts.Keywords: Shift work, performance, alertness, mood, human, circadian rhythms, bright light, melatoninCitation: Smith MR; Fogg LF Eastman CI. A compromise circadian phase position for permanent night work improves mood, fatigue, and performance.SLEEP 2009;32(11):1481-1489.ALERTNESS AND PERFORMANCE DURING NIGHTWORK CAN BE SERIOUSLY IMPAIRED. 1,2 THIS OCCURSBECAUSE THE MASTER CIRCADIAN CLOCK OF MOSTnight workers, which controls the body’s circadian rhythms(e.g., alertness, temperature, melatonin), does not shift to realignwith a night work, day sleep schedule. 3 A sharp increasein sleepiness and decrease in performance occurs around theminimum of the circadian rhythm of body temperature (Tmin),which is usually during the night shift. 4,5 Even with adequatedaytime sleep, night shift decrements remain if the circadianclock is not shifted (e.g., Sharkey et al. 6 ). Consequently, nightwork is associated with safety risks for both the individualworker as well as society. 1,2Alertness and performance during night shifts can be improvedby stimulants such as caffeine 7 and modafinil. 8,9 Brightlight exposure during night shifts can also improve alertnessvia its direct alerting effect. 10 Short naps may also be usefulfor reducing the decrements in night shift alertness. 7 However,none of these interventions can overcome the nadir inthe circadian rhythm of alertness. 7,11 These countermeasuresdo not address the underlying cause of the problem, which ismisalignment between circadian rhythms and the sleep andwork schedule.Submitted for publication February, 2009Submitted in final revised form May, 2009Accepted for publication May, 2009Address correspondence to: Charmane I. Eastman, PhD, BiologicalRhythms Research Laboratory, 1645 W. Jackson Blvd, Suite 425, Chicago,IL 60612; E-mail: ceastman@rush.eduSLEEP, Vol. 32, No. 11, 2009 1481Laboratory and field studies of night work have shown thatscheduled exposure to bright light and darkness (sleep) can beused to shift the circadian clock to completely align with a nightwork, day sleep schedule. 12-16 Complete re-entrainment greatlyimproves alertness and performance during night shifts. 12,17 Despitethe appeal of complete re-entrainment from an alertnessand safety perspective, few night workers are likely to adoptit because the slowness with which the circadian clock adjustsprecludes shifting back to a diurnal schedule on days off. Wehave thus assessed the feasibility of a compromise sleep schedulecombined with interventions to delay the circadian clock toonly partially entrain to the night work, day sleep schedule. Thegoal of partial re-entrainment is to delay the sleepiest circadiantime out of the night work period, into the first portion of thedaytime sleep episodes after work, as well as to maintain it nearthe end of late nighttime sleep episodes on days off. When acompromise phase position is maintained throughout alternationsbetween night shifts and days off, it is conducive of afternoonand evening alertness on days off, as well as alertnessduring night shifts.In a series of 4 studies with alternating blocks of night shiftsand days off, 18-21 we defined the target compromise circadianphase position as a dim light melatonin onset (DLMO) of 3:00.At this phase, the Tmin, an estimate of the sleepiest circadiantime, which occurs about 7 h after the DLMO, 22-24 will fall at~10:00. The sleepiest circadian time would thus be early in thedaytime sleep episodes after night work (daytime sleep startedat 8:30) and late in the sleep episodes on days off (sleep startedat 3:00). The last 2 studies of this series showed that scheduledexposure to bright light and darkness (sleep) delayed the circa-Circadian Phase, Mood, Fatigue and Performance—Smith et al